In the field of semiconductors, fluororesins are widely used due to their excellent heat resistance, chemical resistance and high purity, not only as materials for peripheral parts such as carriers, couplings, tubes, square tanks and the like but also as materials in the area of production and supply of chemicals.
Various researches have been conducted particularly with regard to carriers, due to recent demands for higher purity in processing technologies for semiconductor production. A phenomenon, in which the chemicals and gases that are impregnated into a fluororesin contaminate other chemical tanks or, by gas generation, contaminate wafers, is known as chemical carryover. To prevent this phenomenon, known cleaning methods are, for example, heat treatment at a temperature of 150° C. for 30 minutes, pure-water boiling, heat treatment by nitric acid, etc.
When their cleaning capacity reaches the limit, carriers also reach their application limit and are disposed of. Sometimes carriers reach their application limit due to wear caused by friction, etc., occurring between carrier bodies and wafers.
Generally, as a method for disposing of molded resin parts that have reached their application limit and are no longer in use, various methods for regenerating and reusing the resin parts are proposed in the field of widely used resins such as polyethylene and the like, and some of the methods are already in practical use. However, in the field of fluororesins to which the present invention relates, few methods of regeneration and reuse are known. The inventors are aware of the disclosure of only one method, which is that in Japanese Unexamined Patent Publication No. 300741/1999. Specifically, a fluororesin film composed of a tetrafluoroethylene/ethylene copolymer and used as a covering material for an agricultural greenhouse is washed with a washing liquid and dried; if necessary, surface coatings other than fluororesins are separated and removed by impact compression milling; and then, pellets are produced therefrom by melt extrusion using an extruder.
As described above, few methods have been explored for regeneration and reuse of molded fluororesin articles. The reason is that fluororesin articles have commonly been disposed of into landfills due to their small amount.
However, as the use of fluororesins has recently increased, the disposal amount has also increased. Moreover, from the viewpoint of adapting our societies to recycling, there have been demands for a method for regenerating molded fluororesin articles.
An object of the present invention is to provide a method for producing a recycled fluororesin wherein impurities such as chemical fluids and the like and chemicals are removed to the extent that the same degree remains as is contained in unused fluororesins.